Solid state imaging device and camera system

ABSTRACT

A MOS type solid state imaging device having unit pixels, each having a photodiode a transfer transistor for transferring the signal of the photodiode to a floating node, an amplifier transistor for outputting the signal of the floating node to a vertical signal line, and a reset transistor for resetting the floating node. A gate voltage of the reset transistor is controlled by three values of a power source potential (for example 3V), a ground potential (0V), and a negative power source potential (for example −1V).

RELATED APPLICATION DATA

This application is a continuation of U.S. patent application Ser. No.12/627,425, filed Nov. 30, 2009, which is a continuation of U.S. patentapplication Ser. No. 10/571,720, filed Mar. 13, 2006, the entirety ofwhich is incorporated herein by reference to the extent permitted bylaw. Application Ser. No. 10/571,720 is the Section 371 National Stageof PCT/JP2004/013552. The present application claims priority toJapanese Patent Application No. P2003-323408 filed in the JapanesePatent Office on Sep. 16, 2003.

BACKGROUND OF THE INVENTION

The present invention relates to a solid state imaging device and acamera system, more particularly relates to an X-Y address type solidstate imaging device such as an MOS type solid state imaging device anda camera system using this as the imaging device.

DESCRIPTION OF THE RELATED ART

As an X-Y address type solid state imaging device, for example, an MOStype solid state imaging device, one configured by unit pixels comprisedof three transistors and having a large number of these unit pixelsarrayed in a matrix is known.

The configuration of the unit pixel in this case is shown in FIG. 1. Asapparent from the figure, a unit pixel 100 has a photodiode (PD) 101, atransfer transistor 102, an amplifier transistor 103, and a resettransistor 104.

In the MOS type solid state imaging device employing the above pixelconfiguration, during the period in which the row is not selected, thepotential of a floating node N101 is reduced to a low level (hereinafterdescribed as the “L level”) from a drain line 105 through the resettransistor 104. When the row is selected, an operation for raising thepotential of the floating node N101 to a high level (hereinafterdescribed as the “H level”) is carried out.

In such an MOS type solid state imaging device, as the reset transistor104, use is made of a depression type transistor. This is employed so asto make the drain voltage serving as a power supply of the pixel portionand the potential of the floating node N101 match without variation whenthe reset transistor 104 is on.

Accordingly, the floating node potential when the reset transistor 104is on matches with the potential level of the drain line. As thepotential level of the drain line, specifically, for example asdescribed in Patent Document 1, the H level is a power source potentialVDD, and the L level becomes 0.4 to 0.7V (the L level may be 0V aswell).

Here, consider the potential of the floating node for a selected row anda nonselected row.

First, consider the operation of a selected row.

After the drain line is set at the H level, the reset transistor and thetransfer transistor are sequentially turned off→on→off and a reset phasepotential and a data phase potential are output. A difference of thesesignals is output as a light signal via a correlated double sampling(CDS) circuit.

At the time of acquisition of the data phase potential, when the chargeof the photodiode is transferred to the floating node, the floating nodepotential is lowered.

Next, consider the nonselected row.

Both of the reset transistor and the transfer transistor remain in theoff state as they are. Only the drain line repeats values of H level andL level.

-   Patent Document 1: Japanese Patent Publication No. 2002-51263

SUMMARY OF THE INVENTION

In a past MOS type solid state imaging device, however, since the resettransistor employs a depression structure, even when a reset transistoris in the off state (nonselected row), leakage current causes thefloating node potential to rise (the floating node potential is about 1Vwhen a threshold voltage Vth is −1V).

On the other hand, in a selected row, the floating node potential of thedata phase becomes low in comparison with the potential of the floatingnode potential of the reset phase. When the amount of light isparticularly large, the voltage greatly changes (falls), and thepotential difference from the floating node in the nonselected rowbecomes small.

As a result, the potential signal from a selected row to be set at ahigh potential with respect to a nonselected row is read, but thispotential difference becomes unclear. Therefore, there was the problemthat noise from the nonselected row became large and consequentlyvertical stripes occurred in a bright scene.

Further, similarly due to the employment of the depression structure bythe reset transistor, the influence of the capacity component of thefloating node is visible from a drive circuit of the drain interconnectvia the reset transistor. When the drain interconnect is commonlyconnected to all pixels, it becomes necessary to charge not only thedrain interconnect capacity of all pixels, but also the floating nodecapacity via the reset transistor, so a problem arises from the point ofview of the driver size of the drain line and from the point of view ofthe high speed property.

An object of the present invention is to provide a solid state imagingdevice able to make the noise from a nonselected row small, able tosuppress the occurrence of vertical stripes in a bright scene, notneeding charging including the floating node capacity via a resettransistor, able to prevent an increase of the driver size of the drainline, and able to secure high speed operation and a camera system usingthis as an imaging device.

To achieve the above object, a solid state imaging device of a firstaspect of the present invention has a plurality of unit pixels formed inan imaging area, wherein each unit pixel has a photoelectric converterfor generating a charge in accordance with an amount of incident light,a transfer transistor for transferring a signal of the photoelectricconverter to a floating node, an amplifier transistor for outputting asignal of the floating node to a signal line, and a reset transistor forresetting the floating node, at least one of a plurality of potentialssupplied to a gate electrode of the reset transistor being a negativepotential.

A solid state imaging device of a second aspect of the present inventionhas a plurality of unit pixels formed in an imaging area, wherein theunit pixel has a photoelectric converter for generating a charge inaccordance with an amount of incident light, a transfer transistor fortransferring a signal of the photoelectric converter to a floating node,an amplifier transistor for outputting a signal of the floating node toa signal line, a reset transistor for resetting the floating node, and aportion able to supply three or more types of potentials to the gateelectrode of the reset transistor.

Preferably, the voltage of at least one type of potential among at leastthree or more types of potentials supplied to the gate electrode of thereset transistor is a negative potential.

Preferably, provision is made of a portion able to set the gatepotential when bringing the reset transistor from an ON state to an OFFstate at a negative power source potential after passing a ground levelpower source potential from a positive high level power sourcepotential.

Further, preferably, at both timings of sampling and holding a prechargephase and a data phase, the gate potential of the reset transistor isset at the ground potential.

Further, preferably, in a period during which the gate potential of thereset transistor of the selected pixel is set at the ground potential,the gate potential of the reset transistor of the nonselected pixel is anegative potential.

Preferably, provision is made of a chip for processing the signal outputthrough the signal line.

A camera system according to a third aspect of the present invention hasa solid state imaging device with a unit pixel having a photoelectricconverter for generating a charge in accordance with an amount ofincident light, a transfer transistor for transferring a signal of thephotoelectric converter to a floating node, an amplifier transistor foroutputting a signal of the floating node to a signal line, and a resettransistor for resetting the floating node, at least one of a pluralityof potentials supplied to a gate electrode of the reset transistor beinga negative potential; an optical system for guiding incident light to animaging portion of the solid state imaging device; and a signalprocessing circuit for processing an output signal of the solid stateimaging device.

A camera system according to a fourth aspect of the present inventionhas a solid state imaging device with a unit pixel having aphotoelectric converter for generating a charge in accordance with anamount of incident light, a transfer transistor for transferring asignal of the photoelectric converter to a floating node, an amplifiertransistor for outputting a signal of the floating node to a signalline, a reset transistor for resetting the floating node, and a portionable to supply three or more types of potentials to the gate electrodeof the reset transistor; an optical system for guiding an incident lightto an imaging portion of the solid state imaging device; and a signalprocessing circuit for processing an output signal of the solid stateimaging device.

According to the present invention, a negative potential is applied tothe gate electrode of the reset transistor at the time of nonselection.Due to this, a rising time of the common drain power supply is no longeraffected by the floating node capacity via the depression type resettransistor.

Further, according to the present invention, the gate voltage of thereset transistor is controlled by three values of a power sourcepotential, a ground potential, and a negative power source potential.

For example, instead of directly changing the gate potential from thepower source potential to the negative power source potential, thevoltage of the gate electrode when turning the reset transistor on→offis once held at the ground potential from the power source potential,the ground potential is charged/discharged once, then the potential isset at the negative power source potential.

According to the present invention, the noise from the nonselected rowcan be made small, and the occurrence of vertical stripes in a brightscene can be suppressed.

Further, there are the advantages that there is no need for chargingincluding also the floating node capacity via the reset transistor, theincrease of the driver size of the drain lien can be prevented, and highspeed operation can be secured.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 A view of the configuration of a unit pixel for explaining aproblem of the prior art.

FIG. 2 A circuit diagram showing an example of the configuration of forexample an MOS type solid state imaging device according to anembodiment of the present invention.

FIG. 3 A diagram showing gate potentials of reset transistors and gatepotentials of transfer transistors in a selected row and a nonselectedrow, a common drain power source potential, and a floating nodepotential in a case of operation by a gate voltage of a reset transistorof VRST+ (plus side).

FIG. 4 A diagram showing gate potentials of reset transistors and gatepotentials of transfer transistors in a selected row and a nonselectedrow, a common drain power source potential, and a floating nodepotential in a case of operation by a gate voltage of a reset transistorof two values of VRST+ (plus side) and VRST− (minus side).

FIG. 5 A diagram for explaining a method for driving the gate voltage ofa reset transistor by three values.

FIG. 6 A diagram for explaining the method for driving the gate voltageof a reset transistor by three values and a diagram for explaining amethod for setting sampling and holding of a precharge phase and a dataphase at the ground potential while utilizing a negative potential.

FIG. 7 A diagram for explaining a method combining a method of settingthe potential of a reset transistor at a negative potential through theground level when turning off the reset transistor and a method ofsetting the timing of sampling and holding at the ground level.

FIG. 8 A block diagram showing an example of the configuration of acamera system according to the present invention.

DESCRIPTION OF NOTATIONS

-   -   10 . . . unit pixel, 11 . . . photodiode, 12 . . . transfer        transistor, 13 . . . amplifier transistor, 14 . . . reset        transistor, 22 . . . vertical signal line, 23 . . . drain line,        24 . . . reset line, 25 . . . V-shift register, 26 . . . P-type        MOS transistor, 31 . . . sample & hold/CDS circuit, 32 . . .        horizontal signal line, 34 . . . H shift register.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Below, an embodiment of the present invention will be explained indetail with reference to the drawings.

FIG. 2 is a circuit diagram showing an example of the configuration offor example an MOS type solid state imaging device according to anembodiment of the present invention. Note that, in the MOS type solidstate imaging device, a large number of unit pixels are arrayed in amatrix, but here, for simplification of the drawing, a pixel arraycomprised of two rows and two columns is drawn.

In FIG. 2, a unit pixel 10 has a three-transistor configuration havingthree N-type MOS transistors including a transfer transistor 12, anamplifier transistor 13, and a reset transistor 14 other than forexample a photodiode 11 forming a photoelectric converter.

In this pixel structure, the photodiode 11 converts the incident lightto a signal charge (for example electrons) having a charge in accordancewith the amount of light and stores the charge.

[The transfer transistor 12 is connected between a cathode of thephotodiode 11 and a floating node N11, is connected at its gate to avertical selection line 21, and has a function of transferring a signalcharge stored in the photodiode 11 to the floating node N11 byconduction (ON).

The amplifier transistor 13 is connected between a vertical signal line22 and the power supply Vdd, is connected at its gate to the floatingnode N11, and has a function of outputting the potential of the floatingnode N11 to the vertical signal line 22.

The reset transistor 14 is connected at its drain (one main electrode)to the drain line (interconnect) 23, is connected at its source (othermain electrode) to the floating node N11, is connected at its gate tothe reset line 24, and has a function of resetting the potential of thefloating node N11.

In the pixel area (imaging area) comprised by these unit pixels 10arrayed in a matrix, three lines including the vertical selection line21, the drain line 23, and the reset line 24 are laid in a horizontal(H) direction (left/right direction in the figure) for each row of thepixel array, and the vertical signal line 22 is laid in a vertical (V)direction (up/down direction in the figure) for each column.

Further, the vertical selection line 21, the drain line 23, and thereset line 24 are driven by a V-shift register (VSFR) 25 configuring avertical drive circuit (VDRV).

The vertical selection line 21 and the reset line 24 are directlyconnected to output ends of the V-shift register 25 for outputting avertical selection pulse T and a reset pulse R for each row. The drainline 23 is connected to a reset voltage output end of the V-shiftregister 25 via a P-type MOS transistor 26 for each row. The gate of theP-type MOS transistor is grounded.

In the present embodiment, by driving the reset transistor 14 by threevalues (or four values or more) through the drain line 23, the V-shiftregister 25 provides a potential difference between potentials of thefloating nodes ND11 in the selected row and the nonselected row andclarifies the operations in the two selected row and nonselected row.

For example, in the present embodiment, one of the potentials suppliedto the gate electrode of the reset transistor 14 is at least thenegative potential.

Further, for example, the V-shift register 25 supplies a voltage of atleast one type of potential among at least three types of potentialssupplied to the gate electrode of the reset transistor 14 as thenegative potential.

Further, the V-shift register 25 can set the gate potential whenchanging the reset transistor 14 from the ON state to the OFF state atthe negative power source potential after passing through the groundlevel power source potential from the positive high level power sourcepotential.

Further, in the present embodiment, at both timings of sampling andholding of the precharge phase and the data phase, the gate potential ofthe reset transistor 14 is set at the ground potential.

Further, the V-shift register 25 makes the gate potential of the resettransistor 14 in the nonselected pixel at the negative potential in theperiod during which the gate potential of the reset transistor 14 in theselected pixel is set at the ground potential.

The drive operation of this reset transistor 14 will be explained infurther detail later.

At one side of the vertical direction (up/down direction in the figure)of the pixel area, for each column, a load transistor 27 configured byan N-type MOS transistor is connected between one end of the verticalsignal line 22 and the ground. This load transistor 27 functions as aconstant current source when connected at its gate to a load line 28.

On the other side of the vertical direction of the pixel area, one end(one main electrode) of a sample and hold (SH) switch 29 configured bythe N-type MOS transistor is connected to the other end of the verticalsignal line 22. A control end (gate) of this sample and hold switch 29is connected to an SH line 30.

The other end (other main electrode) of the sample and hold switch 29has an input end of a sample and hold (SH)/CDS (correlated doublesampling) circuit 31 connected to it.

The sample and hold/CDS circuit 31 is a circuit for sampling and holdinga potential Vsig of the vertical signal line 22 and performing thecorrelated double sampling (CDS).

Here, the “correlated double sampling” means processing for sampling twovoltage signals input in time sequence and outputting a differencethereof.

A horizontal selection switch 33 configured by an N-type MOS transistoris connected between the output end of the sample and hold/CDS circuit31 and a horizontal signal line 32.

The control end (gate) of this horizontal selection switch 33 receiveshorizontal scanning pulses H (H1, H2, . . . ) sequentially output at thetime of the horizontal scanning from the H shift register (HSFR) 34configuring the horizontal drive circuit (HDRV).

By the horizontal scanning pulses H being given and the turning on ofthe horizontal selection switch 33, the signal correlated double sampled(CDS) at the sample and hold/CDS circuit 31 is read out through thehorizontal selection switch 33 to the horizontal signal line 32.

This read signal Hsig is derived from an output terminal 36 as an outputsignal Vout through an output amplifier 35 connected to one end of thehorizontal signal line 35.

Below, an explanation will be given of several methods of setting thedrive potential (gate potential) of the reset transistor 14 in thepresent embodiment and their effects including a comparison with aconventional circuit.

Setting Method 1)

In this method, by making it possible to apply a negative potential tothe gate electrode of the reset transistor 14 at the time ofnonselection, the conventional problems can be solved.

FIGS. 3(A) to 3(G) and FIGS. 4(A) to 4(G) are diagrams indicating gatepotentials (RST lines) V24 of the reset transistors and gate potentials(TR lines) V21 of the transfer transistors 12 in the selected row andthe nonselected row, a common drain power source potential V23, and afloating node potential N11 in the case of operation by two values ofthe gate voltage of the reset transistor of VRST+ (plus side) and VRST−(minus side).

FIGS. 3(A) to 3(G) show the case of operation by a gate voltage of thereset transistor of VRST+ (plus side), while FIGS. 4(A) to 4(G) show thecase of operation by a gate voltage of the reset transistor of VRST−(minus side) according to the present embodiment.

Further, in the diagrams, for comparison, the floating node potential ina two-value operation as in the past (gate voltage of reset transistorof VRST+ (plus side) and VRST0 (zero potential)) is shown together.

In the past circuit, as shown in FIGS. 3(A) to 3(G), the rising time t1of the common drain power supply was influenced by the floating nodecapacity via the depression type reset transistor 14 and became long.

According to the method according to the present embodiment, however, asshown in FIGS. 4(A) to 4(G), even in the case where the depression typereset transistor 14 is used, the electric connection via the resettransistor 14 is kept small.

For this reason, the rising time t1 of the common drain power supplybecomes short. Alternatively, the size of the driver of the drain powersupply becomes small. Due to this, a high speed operation and reductionof chip size can be achieved.

Further, in the past circuit, as shown in FIGS. 3(A) to 3(G), due to theinfluence of leakage via the depression type reset transistor, thefloating node potential in the nonselected row rose in the sampling timeof the data phase due to the influence of the drain power supply andacted in a direction making the potential difference between theselected row and the nonselected row smaller.

According to the method according to the present embodiment, however, asshown in FIGS. 4(A) to 4(G), electric coupling via the depression typereset transistor 14 is suppressed, therefore the floating node potentialin the nonselected row does not fluctuate (rise) along with thepotential of the common drain line.

Accordingly, at the timing of the sampling of the data phase, thedifference of the floating node potentials of the selected row and thenonselected row can be clarified.

As a result of this, the occurrence of saturated vertical stripes can besuppressed even when the amount of light is large.

(Setting Method 2)

In this method, by mounting a function of controlling the gate voltageof the reset transistor 14 to the three values of the power sourcepotential (for example 3V), the ground potential (0V), and the negativepower source potential (for example −1V), the conventional problems canbe solved.

As previously explained, in an MOS type solid state imaging device,depression type transistors are used as the reset transistors. Due tothis, there is the merit that the reset variation can be reduced whenthe reset transistors are on.

On the other hand, first, the difference of the floating node potentialsin the nonselected row and the selected row no longer becomes clear and,second, there are the problems of increased speed and greater chip sizefrom the position of the common drain power supply.

Therefore, in the present embodiment, the L level potential of the resettransistor in the nonselected row is set at the negative potential.

In order to supply the negative potential to the MOS type solid stateimaging device, two types of methods including a method of supplying anegative potential from an external power source and a method ofgenerating a negative potential in an internal circuit can beconsidered.

In comparison with the amplitude of the gate of the conventional resettransistor (amplitudes of the power source potential and the groundpotential), when using A negative potential according to the abovemethod, the amplitude thereof becomes large, therefore the amount of thecharging and discharging of the circuit is large, so there is anapprehension that a load will be applied to each potential generationcircuit (or power supply).

Further, for this reason, in the case of a circuit internally generatinga negative potential, it is necessary to make the charge supplycapability larger by exactly the amount of the amplitude. For thisreason, the chip size increases.

Particularly, in the case of a negative power supply generated in theinternal circuit, circuit noise is superimposed on the generatedpotential. The destination of the negative power source potential, thatis, the gate of the reset transistor 14, is capacity coupled with thefloating node N11. Therefore, the fluctuation of the negative powersource potential appears as sensor noise as it is.

In order to solve these problems, in the present embodiment, thefunction of controlling the gate voltage of the reset transistor 14 bythree values including the power source potential (for example 3V), theground potential (0V), and the negative power source potential (forexample −1V) is mounted.

For example, as shown in FIGS. 5(A) to 5(G), for the problem of thecharge supply capability, it is possible to drive the gate potential ofthe reset transistor 14 by three values so as to reduce the load of thenegative power supply generation circuit.

Hitherto, the voltage of the gate electrode when turning the resettransistor on→off was used to directly change the gate potential fromthe power source potential to the negative power source potential.

By making the three-value drive function according to the presentembodiment possible, it is possible to mount the function of holding thevoltage at the ground potential from the power source potential,charging and discharging to the ground potential, and then setting thepotential at the negative power source potential so as to solve theprevious problems.

Simply, when the power supply voltage is 3V, the ground potential is 0V,and the negative power source potential is −1V, the following effectscan be obtained.

When the voltage directly changes from the power source potential to thenegative power source potential as in the past case, if making thecircuit capacity C[F], the amount of charging/discharging becomesQ=C(V1−V2)=4 C, and a load of 4 C is generated in the negative powersupply generation circuit.

On the other hand, when once going through the ground potential, thepotential difference required for draining the negative power supplygeneration circuit is 1V, therefore the amount of charging/dischargingbecomes 1 C, and the load is reduced to ¼ of the load in the pastmethod.

Further, in the case of the negative power supply generated by aninternal circuit, the circuit noise is superimposed on the generatedpotential. The destination of the negative power source potential, thatis, the gate of the reset transistor 14, is capacity coupled with thefloating node N11, therefore the fluctuation of the negative powersource potential appears as sensor noise as it is.

With respect to fluctuation of the negative power source potentialgenerated in an internal circuit, the potential fluctuation of theground potential is small.

By utilizing this, for example, as shown in FIGS. 6(A) to 6(G), in theselected row, the gate electrode potential of the reset transistor isfixed to the ground potential in the timing period of the sampling andholding of the precharge phase and the data phase in the selected row(the gate potential of the reset transistor in the nonselected row istypically fixed to the negative potential).

Due to this, the number of times of change to the negative potentialbecomes small, therefore, not only is the supply load of the negativecharge reduced, but also the effect of noise due to fluctuation of thecapacity coupling property of the floating node potential due to thefluctuation of the potential of the negative power supply generationcircuit is suppressed.

Further, by setting the reset gate at 0V in the selected row and settingthe reset gate at the negative potential in the nonselected row, asignificant difference is reliably added to the floating node potentialsin the selected row and the nonselected row, therefore vertical stripescan be prevented even in a bright scene.

Furthermore, for example as shown in FIGS. 7(A) to 7(G), according to adrive operation combining the method related to FIGS. 5(A) to 5(G) andthe method related to FIGS. 6(A) to 6(G), that is, the method ofreducing the voltage to the negative potential through the ground level(0) when turning off the reset transistor 14 and the method of settingthe timing of sampling and holding to the ground level, two furthereffects are simultaneously obtained.

Next, an example of the operation of the MOS type solid state imagingdevice according to the present embodiment having the aboveconfiguration will be explained. Here, an explanation will be given byfocusing on the bottom left pixel in FIG. 2. The case of employing themethod of controlling the gate voltage of the reset transistor 14 by thethree values of the power source potential (for example 3V), the groundpotential (0V), and the negative power source potential (for example−1V) will be explained as an example.

First, at the time of nonselection, the potential of the floating nodeN1 becomes 0.5V. At this time, a power supply voltage dd, for example3.0V, is output as a reset voltage B1 from the V-shift register 25. Thepotential of the drain line 23 also becomes the power supply voltageVdd.

The load signal given to the load line 28 is set at for example 1.0V,then the reset signal R1 of the H level is output from the V-shiftregister 25. Then, the reset transistor 14 becomes conductive, thereforethe floating node N11 is connected to the drain line 23 through thereset transistor 14, and the potential thereof is reset to the H leveldetermined by a channel voltage of the reset transistor 14, for example2.5V. Due to this, the gate potential of the amplifier transistor 13becomes 2.5V.

A potential Vsig1 of the vertical signal line 22 is determined by thehighest gate voltage among those of the amplifier transistors of theplurality of pixels connected with the vertical signal line 22. As aresult, the potential Vsig1 of the vertical signal line 22 is determinedaccording to the potential of the floating node N11. Specifically, theamplifier transistor 13 forms a source follower together with the loadtransistor 27, and the output voltage thereof appears on the verticalsignal line 22 as the pixel potential Vsig1. The potential Vsig1 at thistime becomes the voltage of the reset level. The voltage of this resetlevel is input to the sample and hold/CDS circuit 31 through the sampleand hold switch 29.

Next, the vertical selection pulse T1 output from the V-shift register25 is raised to the H level. Then, the transfer transistor 12 becomesconductive, and the signal charge (electrons in the present example)converted and stored at the photodiode 11 are transferred (read out) tothe floating node N11. Due to this, the gate potential of the amplifiertransistor 13 changes to the negative direction in accordance with theamount of the signal charge read out from the photodiode 11 to thefloating node N11. The potential Vsig1 of the vertical signal line 22changes in accordance with that.

The potential Vsig1 at this time becomes the voltage of the originalsignal level. The voltage of this signal level is input through thesample and hold switch 29 to the sample and hold/CDS circuit 31. Then,the sample and hold/CDS circuit 31 performs processing for taking thedifference between the voltage at the previous reset level and thevoltage of the signal level this time and holding this differencevoltage.

Next, the reset voltage B1 output from the V-shift register 25 is set to0V. At this time, a reset voltage B1′ given to the pixel 10 through thedrain line 23 is not 0V, but is determined by the channel voltage of theP-type MOS transistor and becomes for example 0.5V.

In that state, when the reset signal R1 of the H level is output fromthe V-shift register 25, the reset transistor 14 becomes conductive,therefore the floating node N11 is connected to the drain line 23through the reset transistor 14, and the potential thereof becomes thepotential of the drain line 23, that is 0.5V, and the pixel 10 returnsto the nonselected state.

At this time, for the gate of the reset transistor 14, when turning thereset transistor 14 on→off through the reset line 24, the gate potentialis not directly changed to the negative power source potential from thepower source potential 3V, but is once held at the ground potential 0Vfrom the power source potential, charged/discharged to the groundpotential, then set at the negative power source potential, i.e., apotential −1V. Due to this, the potential difference required fordraining the negative power source generation circuit becomes 1V, theamount of charging and discharging becomes small, and the load of thecircuit is reduced.

In this nonselected state, the potential of the floating node N11 is not0V, but 0.5V, therefore the leakage of electrons to the photodiode 11through the transfer transistor 12 is prevented. Here, the potential ofthe floating node N1 becomes 0.5V because of the action of the P-typeMOS transistor 26 connected between the reset voltage output end of theV-shift register 25 and the drain line 23.

All pixels in the first row are simultaneously driven by the aboveseries of operations, and one row's worth of signals are simultaneouslyheld (stored) in the sample and hold/CDS circuit 31. Thereafter, theperiod of the photoelectric conversion operation (exposure) at thephotodiode 11 and the storage of photons is entered.

Then, in this photon storage period, the H shift register 34 starts thehorizontal scan operation and sequentially outputs horizontal scanningpulses H1, H2, . . . . Due to this, the horizontal selection switches 33sequentially become conductive and sequentially guide signals held inthe sample and hold/CDS circuit 31 to the horizontal signal line 32.

When performing the same operation for pixels in the second row next,pixel signals of pixels in the second row are read out. By sequentiallyvertically scanning pixels next by the V-shift register 25, pixelsignals of all rows can be read out. By sequentially horizontal scanningthem by the H shift register 34 for each row, signals of all pixels canbe read out.

As explained above, in the MOS type solid state imaging device having athree-transistor configuration in which each unit pixel 10 has atransfer transistor 12, an amplifier transistor 13, and a resettransistor 14, the gate voltage of the reset transistor 14 is controlledby the three values of the power source potential (for example 3V), theground potential (0V), and the negative power source potential (forexample −1V). Therefore, the noise from the nonselected row can be madesmall, and the occurrence of vertical stripes in a bright scene can besuppressed.

Further, there are the advantages that there is no longer a need forcharging including the floating node capacity via the reset transistor,the increase of the driver size of the drain line can be prevented, andhigh speed operation can be secured.

FIG. 8 is a block diagram showing the schematic configuration of acamera system according to the present invention.

The camera system 40 has an imaging device 41, an optical system forguiding incident light to the pixel area of this imaging device 41, forexample a lens 42 for focusing he incident light (imaging light) onto animaging surface, a drive circuit 43 for driving the imaging device 41, asignal processing circuit 44 for processing the output signal of theimaging device 41, and so on.

In this camera system, as the imaging device 41, use is made of a solidstate imaging device according to the above embodiment, that is, an MOStype solid state imaging device having a unit pixel 10 of athree-transistor configuration including a transfer transistor 12, anamplifier transistor 13, and a reset transistor 14 other than thephotodiode 11, where at least one potential supplied to the gateelectrode of the reset transistor is at least the negative potential orthree or more types of potentials can be supplied to the gate electrodeof the reset transistor.

The drive circuit 43 has a timing generator (not shown) for generatingvarious types of timing signals including a start pulse and a clockpulse for driving the V-shift register 25 and the H shift register 34 inFIG. 2 and drives the imaging device (MOS type solid state imagingdevice) 41 in order to realize the drive operation explained in thepreviously explained example of operation. The signal processing circuit44 applies various types of signal processing to the output signal Voutof the MOS type solid state imaging device 41 and outputs the result asthe video signal.

In this way, according to the present camera system, by using the MOStype solid state imaging device according to the previously explainedembodiment as the imaging device 41, the MOS type solid state imagingdevice can make the noise from the nonselected row small, can suppressthe occurrence of the vertical stripes in the bright scene, does nothave to perform charging including the floating node capacity via thereset transistor, can prevent the increase of the driver size of thedrain line, and can secure high speed operation, therefore an imagingimage having a high quality with small noise can be obtained with asmall circuit scale and a low power consumption.

Note that the solid state imaging device of the present invention may bea solid state imaging device formed as one chip or may be a solid stateimaging device of a modular type formed as a set of a plurality of chipsas well. In the case of a solid state imaging device formed as the setof a plurality of chips, it is formed by a sensor chip for the imaging,a signal processing chip for the digital signal processing, and otherchips and sometimes further includes an optical system.

INDUSTRIAL APPLICABILITY

The present invention can make the noise from the nonselected row small,can suppress the occurrence of the vertical stripes in the bright scene,does not have to perform charging including the floating node capacityvia the reset transistor, can prevent the increase of the driver size ofthe drain line, and can secure high speed operation, therefore can beapplied to electronics apparatuses such as digital cameras and videocameras.

1. A solid state imaging device comprising: a plurality of unit pixels formed in an imaging area, each unit pixel having (a) a photoelectric converter for generating a charge in accordance with an amount of incident light, (b) a floating node for storing the charge from the photoelectric converter, and (c) a reset transistor for resetting the floating node; and a plurality of potentials, two of which are supplied to a gate electrode of the reset transistor.
 2. A solid state imaging device as set forth in claim 1, wherein each unit pixel has a transfer transistor for transfer the charge from the photoelectric converter to the floating node.
 3. A solid state imaging device as set forth in claim 1, comprising at least three or more types of potentials, wherein at least one type of the three or more types of potentials supplied to the gate electrode of the reset transistor is a negative potential.
 4. A solid state imaging device as set forth in claim 3, wherein the device has a portion able to set the gate potential when bringing the reset transistor from an ON state to an OFF state at a negative power source potential after passing a ground level power source potential from a positive high level power source potential.
 5. A solid state imaging device as set forth in claim 3, wherein at both timings of sampling and holding a precharge phase and a data phase, the gate potential of the reset transistor is set to the ground potential. 